Kidney stones affect about 5% of the world's population. They occur when abnormally high concentrations of minerals, such as calcium, accumulate in the urinary tract and clump together to form crystals and potentially painful stones.

Most kidney stones contain calcium, and the most common stone type is calcium oxalate. Chinese researchers found that green tea extract bonds to calcium oxalate and makes the resulting crystals a different shape, which makes them less likely to clump together and form large kidney stones.

The smaller crystals and stones are then passed harmlessly through the urine.

In the study, published in CrystEngComm, Xudong Li of Sichuan University in Chengdu, China, and colleagues examined the effects of green tea concentrate on calcium oxalate crystallization using a variety of advanced scanning and imaging techniques.

The results showed that as the amount of green tea extract applied increased, the calcium oxalate crystals became flatter and flatter.

Researchers say flatter crystals form less stable kidney stones that break up more easily.